Cancer cells rely primarily on glycolysis to generate cellular energy and biochemical intermediates for biosynthesis of lipids and nucleotides, while the majority of “normal” cells in adult tissues utilize aerobic respiration. This fundamental difference in cellular metabolism between cancer cells and normal cells, termed the Warburg Effect, has been exploited for diagnostic purposes, but has not yet been exploited for therapeutic benefit.
Pyruvate kinase (PK) is a metabolic enzyme that converts phosphoenolpyruvate to pyruvate during glycolysis. Four PK isoforms exist in mammals: the L and R isoforms are expressed in liver and red blood cells, the M1 isoform is expressed in most adult tissues, and the M2 isoform is a splice variant of M1 expressed during embryonic development. All tumor cells exclusively express the embryonic M2 isoform. A well-known difference between the M1 and M2 isoforms of PK is that M2 is a low-activity enzyme that relies on allosteric activation by the upstream glycolytic intermediate, fructose-1,6-bisphosphate (FBP), whereas M1 is a constitutively active enzyme.
All tumor cells exclusively express the embryonic M2 isoform of pyruvate kinase, suggesting PKM2 as a potential target for cancer therapy. PKM2 is also expressed in adipose tissue and activated T-cells. Thus, the modulation (e.g., inhibition or activation) of PKM2 may be effective in the treatment of, e.g., obesity, diabetes, autoimmune conditions, and proliferation-dependent diseases, e.g., benign prostatic hyperplasia (BPH). Current modulators (e.g., inhibitors) of pyruvate kinase are not selective, making it difficult to treat disease related to pyruvate kinase function.
Furthermore, phosphotyrosine peptide binding to PKM2 leads to a dissociation of FBP from PKM2 and conformational changes of PKM2 from an active, tetrameric form to an inactive form. Compounds that bind to PKM2 and lock the enzyme in the active confirmation will lead to the loss of allosteric control of PKM2 needed for shunting biochemical intermediates from glycolysis into biosynthesis of nucleotides and lipids. Thus, the activation of PKM2 can also inhibit the growth and proliferation of cancer cells, activated immune cells, and fat cells.
There is a continuing need for novel treatments of diseases such as cancer, diabetes, obesity, autoimmune conditions, proliferation-dependent diseases (e.g., BPH), and other diseases related to the function of pyruvate kinase (e.g., PKM2).